Inclusion Criteria

• Diagnosis of type 2 diabetes mellitus currently treated with metformin alone but, experiencing inadequate glycemic control. The subject should have received the metformin monotherapy for at least the 3 months prior to Screening; and must have a stable dose of greater than or equal to 1500 mg metformin for at least 8 weeks prior to randomization. Subjects with a maximum tolerated dose that is documented to be less than 1500 mg of metformin may also be enrolled if this dose has been stable for 8 weeks prior to randomization.
• No treatment with antidiabetic agents other than metformin within the 3 months prior to Screening. (Exception: if a subject has received other antidiabetic therapy for less than 7 days within the 3 months prior to Screening.)
• Body mass index greater than or equal to 23 kg/m2 and less than or equal to 45 kg/m2
• Fasting C-peptide concentration greater than or equal to 0.8 ng per mL. (If this screening criterion is not met, the subject still qualifies if C-peptide is greater than or equal to 1.5 ng per mL after a challenge test.
• Glycosylated hemoglobin concentration between 7.0% and 10.0%, inclusive
• If regular use of other, non-excluded medications, must be on a stable dose for at least the 4 weeks prior to Screening. However, as needed use of prescription or over-the-counter medications is allowed at the discretion of the investigator.
• Systolic blood pressure less than or equal to 180 mm Hg and diastolic pressure less than or equal to 110 mm Hg
• Hemoglobin greater than or equal to 12 g per dL for males and greater than or equal to 10 g per dL for females
• Alanine aminotransferase less than or equal to 3 time the upper limit of normal
• Serum creatinine less than1.5 mg per dL for males and less than 1.4 mg per dL for females
• Thyroid-stimulating hormone level less than or equal to the upper limit of the normal range and the subject is clinically euthyroid.
• Neither pregnant nor lactating.
• Female subjects of childbearing potential must be practicing adequate contraception. Adequate contraception must be practiced for the duration of participation in the study.
• Able and willing to monitor their own blood glucose concentrations with a home glucose monitor
• No major illness or debility that in the investigator's opinion prohibits the subject from completing the study
• Able and willing to provide written informed consent

Exclusion Criteria

• Urine albumin to creatinine ratio of greater than 1000 μg per mg at Screening. If elevated, the subject may be rescreened within 1 week.
• History of cancer, other than squamous cell or basal cell carcinoma of the skin, that has not been in full remission for at least 5 years prior to Screening. (A history of treated cervical intraepithelial neoplasia I or cervical intraepithelial neoplasia II is allowed.)
• History of laser treatment for proliferative diabetic retinopathy within the 6 months prior to Screening
• History of treated diabetic gastric paresis
• New York Heart Association Class III or IV heart failure regardless of therapy. Currently treated subjects who are stable at Class I or II are candidates for the study.
• History of coronary angioplasty, coronary stent placement, coronary bypass surgery, or myocardial infarction within the 6 months prior to Screening
• History of any hemoglobinopathy that may affect determination of glycosylated hemoglobin
• History of infection with hepatitis B, hepatitis C, or human immunodeficiency virus
• History of a psychiatric disorder that will affect the subject's ability to participate in the study
• History of angioedema in association with use of angiotensin-converting enzyme inhibitors or angiotensin-II receptor inhibitors
• History of alcohol or substance abuse within the 2 years prior to Screening
• Receipt of any investigational drug within the 30 days prior to Screening or a history of receipt of an investigational antidiabetic drug within the 3 months prior to Screening
• Prior treatment in an investigational study of SYR-322

• Excluded Medications:

  • Treatment with antidiabetic agents other than study drug or metformin is not allowed within the 3 months prior to Screening and through the completion of the end-of treatment/early termination procedures.
  • Treatment with weight-loss drugs, any investigational antidiabetics, or oral or systemically injected glucocorticoids is not allowed from 3 months prior to randomization through the completion of the end-of-treatment/early termination procedures. Inhaled corticosteroids are allowed.
  • Subjects must be instructed not to take any medications, including over-the-counter products, without first consulting with the investigator.